Aristotle (384-322 B.C.) studied at Plato's Academy for twenty years. After a few years in Macedonia as a tutor to the future Alexander the Great, Aristotle returned to Athens and established his own school, the Lyceum. His presentation of courses was encyclopedic. Unlike Plato, Aristotle had an abiding interest in natural science and wrote extensively in physics, zoology, and psychology. Much as Socrates had been charged with impiety, so also Aristotle was charged—in large measure due to his former relationship with Alexander. Unlike Socrates, Aristotle fled Athens, "lest," as he is quoted, "the Athenians sin twice against philosophy." His work in logic was not significantly improved upon until the development of symbolic logic in the twentieth century. The central concepts of his poetics and ethics still remain influential. Charles Darwin once wrote, "Linnaeus and Cuvier have been my two gods…but they were mere schoolboys [compared to] Aristotle."

In the Nicomachean Ethics,[1] Aristotle argues that what we seek is eudaimonia, a term translated in this reading as "happiness."Eudaimonia is better expressed as "well-being" or "excellence of performing the proper function." When Aristotle explains human virtue, he is not discussing what we now refer to as (Victorian) virtue. He is clarifying the peculiar excellence of human beings in the same manner as we often speak of the peculiar excellence attributable to the nature of a thing. For example, a tool is useful in virtue of the fact that it performs its function well. Aristotle's purpose in the Nicomachean Ethics is not just to explain the philosophy of the excellence for human beings but also to demonstrate specifically how human beings can lead lives of excellence as activity in accordance with practical and theoretical reason.